May 16, 2006
Europa Caught in the Middle
Europa displays a frozen record of
strikes by Jupiter's thunderbolts in the recent past. Jupiter's
thunderbolts preferred to run across the surface of Europa rather than
through the near vacuum of space.
If the ancient thunderbolt legends are taken at
face value, then we are faced with the possibility that our neighboring
planets waged celestial wars with thunderbolts in the time of human
myth-makers. If this happened, what "smoking guns" should we expect to
Jupiter's moon, Europa, offers an excellent
example. The images above show a plasma ball as an electric discharge
flows across it (top) and a view of Europa's scarred surface (bottom).
Europa's rotation has been captured by Jupiter, so the same side faces
Jupiter all the time. (The same is true of our own moon and the Earth.)
The parts of Europa directly facing Jupiter and those exactly opposite
are rugged and chaotic (hence the name chaos regions). These regions are
where the thunderbolts struck and where they departed. The surface areas
connecting the two chaos regions (bottom image) are characterized by
long, looping scars in patterns similar to those seen on the plasma
Europa displays a frozen record of strikes by
Jupiter's thunderbolts in the recent past. Just as lightning looks for
the easiest path to ground, Jupiter's thunderbolts preferred to run
across the surface of Europa rather than through the near vacuum of
space. The result is a filamentary pattern of superimposed furrows
running this way and that for hundreds and thousands of kilometers
across the face of the moon.
Europa was not a target itself, but it bears the
scars from being caught in the crossfire. Even if future missions to
Europa discover continued "erosion" by tidal or electrical connections
with Jupiter, most of the scars we see today were created in brief
catastrophic episodes, not gradually at a uniform rate.
As the surface lightning blasted its way across
the moon, it heaped material to either side to form levees. It ripped
across earlier channels as if they were not there. Jupiter's lightning
was so powerful that it converted some of the oxygen in the water ice to
sulfur--creating the dark coloration down the center and to either side
of the large furrows.
Europa is completely covered with this type of
plasma scarring, and other moons are partially covered with similar
patterns. Among them are Jupiter's Ganymede and Callisto, Saturn's
Enceladus, and Uranus' Miranda. Continued study of these moons offers an
opportunity to learn more about the recent electrical history of the
solar system and our own human heritage.
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